Ordovician arc collision and foredeep evolution in the Gaspé Peninsula, Québec: the Taconic Orogeny in Canada and its bearing on the Grampian Orogeny in Scotland

Abstract

The Middle to Upper Ordovician Deslandes, Cloridorme and Garin Formations in the eastern Gaspé Peninsula, Québec, are some of the most extensively exposed foredeep successions along the northern Appalachian portion of the Taconic–Caledonian orogen. Their depositional and biostratigraphic frameworks ( N. gracilis to C. spiniferus Zones, approximate correlatives to the N. gracilis to D. clingani British Zones) indicate that foredeep evolution spanned c. 10 Ma and was essentially synchronous with the convergence and accretion of the Popelogan arc to the Laurentian margin during the Caradoc ( c. 458–449 Ma). These results, when combined with metamorphic and radiometric age data synthesized from across the Laurentian segments of the northern Appalachian and northwestern Ireland Taconic–Caledonian orogen, further substantiate that orogenesis consisted of several short‐lived ( c. 10–20 Ma) deformational episodes confined to Arenig through Ashgill time ( c. 485–440 Ma). This indicates that the total duration of orogeny, as recorded by arc magmatism, metamorphism and Laurentian foredeep development, spanned no more than c. 45 Ma. In that the Scottish Caledonides are a consanguineous part of this orogen, their tectonostratigraphic evolution, i.e., Grampian Orogeny, should be similar. Accordingly, the results detailed above are geodynamically compatible with and thereby support tectonic models that define the Grampian Orogeny in Scotland as a mostly Early to Mid‐Ordovician ( c. 480–460 Ma) tectonic episode of short, rather than long duration.